1. Field of the Invention
The present invention is generally in the field of circuits. More specifically, the invention is in the field of amplifier circuits.
2. Background Art
Direct conversion receiver architectures are desirable in radio designs because they are able to down-convert an incoming Radio Frequency (“RF”) signal to an Intermediate Frequency (“IF”) signal, thereby eliminating the need for external RF/IF filter blocks and consequently reducing the cost of the receiver. However, direct conversion receivers typically suffer from random DC offset voltages which may be caused by local oscillator self mixing and DC offsets present in the active amplifier stages. These random DC offset voltages can undesirably saturate the active amplifier stages.
In order to reduce the DC offset voltages, a feedback loop is typically used around the active amplifier stage to suppress the DC offset voltages. A conventional feedback loop operates by monitoring the output of the amplifier stage and by providing a correction voltage at the input of the amplifier stage. However, to avoid cancellation of any desired input signals, the feedback loop must be band-limited. Since the bandwidth of the feedback loop changes with the gain of the amplifier stage, the gain of the amplifier stage must remain fixed for the bandwidth of the feedback loop to remain constant. As such, in applications where the gain of the amplifier stage is continuously varied by an analog control signal, the conventional feedback loop cannot maintain a constant bandwidth to provide proper DC offset correction.
Accordingly, there is a need in the art for a system and method for DC offset correction of an amplifier using feedback loops which maintain a constant bandwidth as the gain of the amplifier is continuously varied.